Rear wheel drive automatic transmission with a selectable one-way clutch

ABSTRACT

A vehicle includes a rear-wheel drive (RWD) automatic transmission having a stationary member, a two-mode selectable one-way clutch (SOWC), pressurized fluid, and a valve body assembly (VBA). The VBA has a piston, a return spring, and an actuator linkage in contact with the piston and a shift lever of the SOWC. Fluid moves the piston and linkage in one direction to lock the SOWC and enable a reverse mode having no spin losses, and the spring moves the piston and linkage in another direction to unlock the SOWC in a forward mode. A method reduces spin losses by admitting fluid into the VBA to move the piston in one direction to thereby rotate the shift lever of the SOWC to one angular position to lock a driving member of the transmission to the stationary member during reverse, engine braking first gear, and manual low speeds.

TECHNICAL FIELD

The present invention relates to a six-speed rear wheel drive (RWD)automatic transmission having a selectable one-way clutch (SOWC) that isselectively engaged in one or more predetermined operating modes.

BACKGROUND OF THE INVENTION

In certain rear wheel drive (RWD) vehicle transmissions, such as in asix-speed RWD automatic transmission of the type known in the art havingthree gear sets and five torque transmitting elements or clutches, oneof the five clutches can be applied in engine braking first gear, manuallow, and reverse transmission operating modes. Therefore, such a clutchis referred to functionally as a “low and reverse clutch”, and isselectively engaged or disengaged to enable the operating modes listedabove. The input member of the low and reverse clutch can also beselectively connected to a conventional one-way clutch in order toselectively prevent relative rotation of members of two of the gearseats of the transmission when engaged.

In all other forward gears, i.e., in second-through-sixth gear in theconventional six-speed RWD automatic transmission mentioned above,reaction torque does not act on the one-way clutch due to theapplication or engagement of one or more of the four other clutches inthe transmission. Consequently, the one-way clutch rotates freely or“freewheels”, that is, with relative motion being present between theinput and output members of the low and reverse clutch. Moreover, therelative speed of such rotation tends to increase with each successivegear change.

As is known in the art, a disengaged multi-plate clutch can produce dragor spin losses whenever relative motion is present between the input andoutput members of the multi-plate clutch. The spin losses can in turnreduce fuel economy. As the low and reverse clutch is disengaged in mostof the forward gears of the RWD transmission described above, except forengine braking first gear and manual low, and as most of the time such atransmission operates in one of these forward gear ratios, a modest butmeasurable amount of the spin loss occurs when the low and reverseclutch is disengaged.

SUMMARY OF THE INVENTION

Accordingly, a rear-wheel drive (RWD) vehicle having a six-speed RWDautomatic transmission is provided having five torque-transmittingmechanisms or clutches and three gear sets. The transmission has areverse speed, and the six speeds include five forward high speeds and afirst gear speed. First gear in turn includes a manual low speed and anengine braking first gear speed. The transmission includes a valve bodyassembly (VBA) and a two-mode selectable one-way clutch (SOWC) as one ofthe five clutches. Within the scope of the invention, the SOWC replacesthe low and reverse clutch and the conventional one-way clutch describedabove, while a conventional VBA is modified to include a SOWC controlmechanism adapted to select between the two modes of the SOWC, forwardand reverse, in the engine braking first gear, reverse, and in a manuallow gear speeds.

When a transmission control algorithm commands or signals a mode changeor shift to one of the engine braking first gear, reverse, or manual lowgears, pressurized fluid enters the piston bore. The piston moves fromthe top of the piston bore to the bottom of the piston bore, thuscompressing the return spring and simultaneously moving the actuatorlinkage to the second position. When the transmission algorithm commandsor signals a mode change or shift to one of the second-through-sixthgears, and first gear other than manual low and engine braking,pressurized fluid exits the piston bore, and the return spring moves thepiston to the top of the piston bore.

The VBA is located below the rotating torque elements of thetransmission, and is aligned with and secured to the underside of thetransmission case. The control mechanism portion of the VBA includes abore housing on or within an upper surface of the VBA, with the borehousing defining a piston bore as well as a spring bore. The piston borecontains a hydraulically-actuated piston, the movement of whichultimately moves an interconnected actuator mechanism or linkage whichcontrols the rotational movement of a selector plate within SOWC. Thecenterline of the piston bore is perpendicular to the axis of rotationof the transmission, and is ideally located in the same plane as therotational arc of the selector plate of the SOWC, although other planarconfigurations are also usable within the scope of the invention.

The piston is in continuous contact with or connected to the actuatorlinkage, which can be configured as a plate, a rod, or any othersuitable linkage. The actuator linkage engages the selector plate of theSOWC by retaining or engaging a shift lever that is attached to theselector plate, or that is an appendage thereof. An energy storagedevice, such as a compression spring or other style of return spring,exerts a return/biasing force on the piston to bias the piston in afirst position, with fluid pressure to the VBA moving the piston to asecond position. The first position corresponds to a first angularposition of the selector plate of the SOWC, which is maintained onlyduring one or more predetermined forward operating modes, i.e., thefirst-through-sixth gears, other than engine braking first gear andmanual low. The second corresponds to a second angular position of theselector plate, which is maintained only during one or more otheroperating modes, i.e., the engine braking first gear speed, the reversegear speed, and the manual low gear speed.

A method for reducing spin losses in a six-speed RWD automatictransmission is also provided. The transmission has a SOWC that iscontrolled via a selection mechanism integrated into the VBA, with theSOWC replacing the conventional low and reverse clutch assembly andone-way clutch. The method includes detecting, sensing, or otherwisedetermining a shift command signaling a requested shift of thetransmission to a reverse, engine braking, or manual low speeds, andadmitting pressurized fluid into the VBA described above in response tothe shift command. Pressurized fluid moves the piston in one direction,and thus moves the shift lever of the SOWC to lock a driving member ofthe transmission to a stationary member. In this manner, spin losses inthe transmission are reduced in the transmission.

The above features and advantages, and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic illustration of a vehicle in accordance with theinvention;

FIG. 2 is a partial cutaway sectional view of an automatic six-speed RWDautomatic transmission usable with the vehicle of FIG. 1;

FIG. 3 is a schematic exploded perspective view of the transmission ofFIG. 2;

FIG. 4 is a schematic perspective view of a portion of a valve bodyassembly (VBA) usable with the transmission of FIGS. 2 and 3; and

FIG. 5 is a schematic perspective view of an integrated controlmechanism usable with the VBA and transmission of FIGS. 2, 3, and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the Figures, wherein like reference numerals refer tolike or similar components throughout the several figures, and beginningwith FIG. 1, a vehicle 10 includes an engine (E) 12, such as a gasoline,diesel, or alternative fuel internal combustion engine, although otherpower sources may be used within the scope of the invention. Forexample, the engine 12 could be also or alternatively configured as abattery or a fuel cell-powered electric motor, or another alternativepower source to the conventional internal combustion engine. The engine12 is connected to an automatic transmission (T) 14 via an input memberor shaft 11. The transmission 14 transmits a rotational force or torqueto an output member or shaft 13, which ultimately propels the vehicle 10via a set of road wheels 17.

Referring to FIG. 2, the transmission 14 has three gear sets, which arelabeled G1, G2, and G3 is FIG. 2 for clarity. The transmission 14 alsohas five clutches, four of which are labeled C1-C4 for clarity, with thefifth clutch being configured as a two-mode selectable one-way clutch(SOWC) 16. The gear sets G1, G2, and G3 respectively are an input gearset, a front output gear set, and rear output gear set. The gears setsG1-G3, the clutches C1-4, and the SOWC 16 can be selectively engaged anddisengaged alone or in various combinations to provide a six-speedrear-wheel drive (RWD) functionality, as will be understood by those ofordinary skill in the art.

The transmission 14 also includes an outer housing or case 20, as wellas a valve body assembly (VBA) 22 having an integrated SOWC controlmechanism 24, as described in detail below with reference to FIGS. 4 and5. As used herein, the term “integrated” refers to the relativeconfiguration of the SOWC control mechanism 24 and the VBA 22, with thecontrol mechanism 14 being a portion or integral part of the VBA 22. Thecontrol mechanism 24 selectively controls or actuates the SOWC 16 basedon one or more predetermined operating modes of the transmission 14, asdescribed below.

As will be understood by those of ordinary skill in the art, a SOWC issimilar to a conventional one-way clutch in basic operation. However,depending on the details of the design, a SOWC is also capable ofproducing a mechanical connection between a given “driving” member, suchas an input race or a first coupling plate, to a second independent“driven” member, such as an output race or second coupling plate in oneor both rotational directions. Also depending on the design, a SOWC canoverrun in one or both directions of rotation. Typically, a SOWCcontains a selector ring or plate that when moved to a second or a thirdposition, controls or selects the various operating modes of the SOWC.

The mechanical means used to lock a SOWC such as the SOWC 16 of FIG. 1are varied and well known. For example, a SOWC may use rollers, sprags,rockers, struts, or another suitable torque-transmitting element, aplurality of which are positioned between the input and output races ormembers of the SOWC 16. Depending on the particular type or style ofSOWC used and the required direction of rotation, each race of the SOWCmay contain unique surface features, such as windows or strut wells,each being suitable for engaging one or more of the torque-transmittingelements positioned therein in order to selectively enable variousclutch operating modes.

In the transmission 14 of FIG. 2 in particular, the SOWC 16 has an innerrace or driving member 26 and an outer race or driven member 28. Thedriven member 28 is affixed or grounded to the center support 30, suchas by engaging a plurality of splines 33 with mating splines 37 in thecenter support 30. The driving member 26 is connected to the output gearsets G2 and G3, such as but not limited to a carrier member of aplanetary gear set. The SOWC 16 can selectively transmit torque betweenthe driving member 26 and the driven member 28 in one rotationaldirection. Reversing the direction of rotation of the driving member 26in turn enables the driving member 26 to freewheel with respect to thedriven member 28.

The VBA 22 is positioned adjacently to and below the axis or centerline27 of the SOWC 16 such that fluid pressure admitted to the VBA 22 asexplained above moves the shift lever 40 of the SOWC 16 in onedirection, ultimately engaging the SOWC 16 in a reverse mode of thetwo-mode SOWC 16. Discharge of the fluid pressure from the VBA 22 movesthe shift lever 40 in another direction, ultimately disengaging the SOWC16 to enable the forward high operating modes, usable with thefirst-through-sixth gears of the transmission 14, other than manual lowand engine braking first gear speeds. Thus, the SOWC 16 can be engagedin three transmission operating modes: reverse gear speed, manual lowgear speed, i.e., when an operator moves a shift lever to the “L”position, and engine braking first gear speed, i.e., which occurs forshort time when the shift lever is in the “D” position and thetransmission 14 is launching the vehicle 10 of FIG. 1 from a standstillin first gear up to approximately 5 miles per hour.

Referring to FIG. 3, an exploded view of a portion 14A of thetransmission 14 of FIG. 2 shows the general orientation of the VBA 22,the case 20, and the SOWC 16. The VBA 22 having the control mechanism 24is positioned adjacently to an underside or bottom surface 31 of thecase 20, i.e., below a centerline 27 of the transmission 14, which inone embodiment can be at least partially within a cavity (not shown)defined by the case 20 in order to minimize packaging space. The SOWC 16is positioned or enclosed by the center support 30 of the transmission14. The driven member 28 is held stationary, i.e., is grounded orconnected to the center support 30, such as by engaging the varioussplines 33 of the driven member 28 with a plurality of mating splines 37of the center support 30.

A suitably shaped and/or sized linkage, arm, or shift lever 40 of theSOWC 16 is integrally formed with or directly or indirectly connected toa selector ring or plate (not shown) of the SOWC 16, and extendsradially-outward from the SOWC 16 toward the control mechanism 24 of theVBA 22. The shift lever 40 can be configured with a shaped end 44 asdescribed below, such as a fork as shown in FIG. 3, with the shaped endbeing shaped, sized, or otherwise configured so as to mesh with orengage an actuator linkage 50 within the control mechanism 24. The SOWC16 may also include a pair of retaining rings 48, 49 for respectivelysecuring the SOWC 16 within the center support 30 within a desiredtolerance.

Referring to FIG. 4, a perspective view of the VBA 22 with certainsurfaces removed for clarity shows the internal detail of the controlmechanism 24. As described above, the control mechanism 24 is anintegral portion of the VBA 22, and includes a bore housing 56. The borehousing 56 is formed integrally with, or is otherwise connected to, anupper surface 57 of the VBA 22, with the bore housing 56 having a springend 62 and a piston end 64 generally describing the separate functionalportions or ends of the bore housing 56. At the piston end 64 is apiston bore 58 containing an apply piston 66, and at the spring end 62is a spring bore 59 containing a return spring 76.

The piston bore 58 is machined to receive the apply piston 66 in aclose-fitting but freely movable manner. The piston 66 is selectivelyactuated in the direction of arrow A by an inlet of pressured fluid,represented in FIG. 4 by the arrow I, through an inlet port 68.Likewise, an exhaust port 74 is provided in the piston bore 58 to allowany trapped fluid to escape, as indicated by the arrow O, therebypreventing the piston 66 from becoming hydraulically locked. A stopfeature 70, such as but not limited to a bumper or stop pin, preventsthe piston 66 from blocking the flow of hydraulic fluid into the inletport 68. Within the scope of the invention, a similar feature could alsobe incorporated into a piston bore plug 72 instead of the piston 66.

The piston 66 is in direct continuous contact with and/or operativelyconnected to the actuator linkage 50, which is itself connected to theshift lever 40, and ultimately to the SOWC 16, as shown in FIG. 5 anddescribed below. Due to packaging limitations, the actuator linkage 50,the piston 66, and a return spring 76 can be positioned in differentplanes, or alternately can be coplanar as shown in FIGS. 3-5. Howeverconfigured, movement of the piston 66 in the direction of arrow A pushesor moves the actuator linkage 50 in the same direction. When the inletfluid pressure is discontinued, the return spring 76 within the springbore 59 pushes or moves the piston 66 in the direction of arrow B (seeFIG. 5), a movement that exhausts or discharges fluid through backthrough the inlet port 68.

The stroke length of the piston 66 is preferably slightly shorter thanthe chordal length of the total rotational angle of the shift lever 40(see FIG. 5) at a centerline 87 of the spring bore 59. If the pistonstroke is greater than the chordal length, certain components in theSOWC 16 such as the selector plate (not shown) would become the reactionmembers for the apply force in the direction of arrow A (see FIG. 5)from the piston 66, as well as the return force in the direction ofarrow B (see FIG. 5) from the return spring 76. By minimizing thereaction forces transmitted to the SOWC 16, wear is reduced, whichpotentially prolongs the life of the SOWC 16. Conversely, if the pistonstroke was much less than the aforementioned chordal length, the modechanges in the SOWC 16 may not be fully or optimally implemented.

The control mechanism 24 is positioned on the upper surface 57 of theVBA 22, with the centerline 87 of the bore housing 56 in the same planeas the rotational arc of the selector plate (not shown) in the SOWC 16.A window 80 is cast, machined, or otherwise provided in the bore housing56 and centered on a vertical axis or line 81 (see FIG. 5) of the SOWC16 that passes through the rotational axis 27 of the SOWC 16 (see FIG.5). The window 80 serves as a sufficient opening to allow the shiftlever 40 (see FIG. 5) of the SOWC 16 to engage or mesh with the actuatorlinkage 50.

Still referring to FIG. 4, a wall 82 in the piston bore 58 acts as hardstop and thus limits piston travel of the piston 66 when fluid from afluid control channel 88 and the inlet port 68 is directed into thepiston bore 58. The bore plug 72 closes an outboard end of the pistonbore 58, and can be secured in place by a plug retaining ring 90. Thebore plug 72 can also act as a hard stop to limit piston travel in theoutboard direction.

Within the spring bore 59, the return spring 76 is radially-retained,with the return spring 76 being configured as, for example, a helicalcompression type spring, although other spring designs are usable withinthe scope of the invention. A retaining ring 91 can be installed in thespring bore 59 behind a support sleeve 92 to act as a first reactionmember for the spring force provided by the return spring 76. When usinga support sleeve 92, one end of the return spring 76 is in contact withthe support sleeve 92, while the other end of the return spring 76 is incontact with one of a pair of collars 93.

The spring force from the return spring 76 urges the piston end 64 ofthe actuator linkage 50 into direct continuous contact with the piston66. The actuator linkage 50 and the piston 66 both move in the borehousing 56 until the stop feature 70 contacts the bore plug 72. Sincethe shaped end 44 of the shift lever 40 (see FIG. 5) is engaginglyrestrained between the pair of collars 93, the selector plate (notshown) of the SOWC 16 is held in the first angular position 94 (see FIG.5). The plug retaining ring 90 is the second reaction member for thespring force. Because the piston 66 is a separate part from the actuatorlinkage 50, it is isolated from any couple or radial force generated inthe latter. This reduces wear or scuffing between the piston 66 and thepiston bore 58, and thus minimizes the risk of any of the parts bindingin the bore housing 56.

Referring to FIGS. 4 and 5 together, when a mode change is required ofthe SOWC 16, and in particular when the SOWC 16 is to be applied orengaged, pressurized fluid from a transmission pump (not shown) or adedicated pump is directed into the fluid control channel 88, and thenenters the piston bore 58 through the port 68. As any hydraulic forceacting in the direction of arrow A on the piston 66 exceeds a returnforce provided in the direction of arrow B by the return spring 76, thepiston 66 and the actuator linkage 50 move together towards the springend 62 of the bore housing 56 until the piston 66 contacts the wall 82at the bottom of the piston bore 58. Because the shaped ends 44 on theshift lever 40 (see FIG. 5) are trapped or positioned between the pairof collars 93, the shift lever 40 and the selector plate (not shown) ofthe SOWC 16 each rotate around the rotational axis 27 of the SOWC 16(see FIG. 5) to a second angular position 96, thereby affecting therequired mode change or shift in the SOWC 16. Once positioned at thesecond angular position 96, the SOWC 16 is set or engaged in a reversemode, wherein no relative motion is possible between the driving member26 and the driven member 28 (see FIGS. 2, 3, and 5) in either rotationaldirection.

To return the SOWC 16 to its other mode, i.e., the forward mode,pressurized fluid is exhausted from the fluid control channel 88. As thereturn force provided by the return spring 76 exceeds that of theexhausting fluid, the piston 66 and the actuator linkage 50 move in thedirection of arrow B toward the piston end 64 of the bore housing 56.

Referring to FIG. 5, the bore housing 56 has a centerline 87 in the sameplane as the rotational arc of the selector plate (not shown) of theSOWC 16. The first and second angular positions 94 and 96 of theselector plate (not shown) of the SOWC are substantially equidistantfrom the vertical centerline or axis 81 of the SOWC 16. To facilitateassembly into the case 20 (see FIG. 2), the shift lever 40 and/or theshaped end 44 thereof can be configured so as to be removable from theselector plate (not shown) and the SOWC 16. For example, the shift lever40 can be inserted into a groove or slot in the selector plate, with theshift lever 40 prevented from moving once secured or retained to theactuator linkage 50.

In this manner, spin losses are reduced in the transmission in thefirst-through-sixth gear transmission operating modes. Also, the weightand packaging space of the transmission is reduced, as all of theconventional low and reverse clutch components are eliminated, such as aclutch plate assembly, a clutch apply piston, and a clutch returnspring. The reverse mode of the SOWC 16 replaces the functionality ofthe low and reverse clutch, while the forward mode of the SOWC 16behaves in the same manner as the one-way clutch it replaces.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A rear wheel drive (RWD) vehicle comprising: a six-speed transmissionhaving three gear sets and five clutches, the five clutches including atwo-mode selectable one-way clutch (SOWC) having a driving member and astationary member, wherein the five clutches can be selectively engagedto connect members of the three gear sets to the stationary member tothereby enable a reverse speed and the six speeds of the transmission,the six speeds including: an engine braking first gear speed, a manuallow speed, a first gear speed, and five forward high speeds; pressurizedfluid; and a valve body assembly (VBA) having an integrated controlmechanism operable for controlling the SOWC to thereby select betweenthe two modes of the SOWC, the integrated control mechanism including: afirst bore and a second bore, wherein the first bore is in fluidcommunication with the source of pressurized fluid and has a centerlinethat is positioned below an axis of rotation of the SOWC; an applypiston positioned within the first bore and moveable therein; a returnspring positioned within the second bore and compressible therein; anactuator linkage in continuous contact with the apply piston and thereturn spring; and a shift lever operatively connected to each of theSOWC and the actuator linkage, the shift lever being operable forselecting between the two modes of the SOWC in response to a directionof motion of the apply piston; wherein the pressurized fluid moves theapply piston and actuator linkage in one direction to thereby lock thedriving member to the stationary member, and to thereby select one ofthe engine braking first gear speed, the reverse speed, and the manuallow speed; and wherein the return spring moves the apply piston and theactuator linkage in another direction to unlock the driving member fromthe stationary member during one of the first gear speed and the fiveforward high speeds.
 2. The vehicle of claim 1, wherein the stationarymember is a driven member of the SOWC that is indexed to a stationarycase of the transmission.
 3. The vehicle of claim 1, wherein the shiftlever includes a shaped end adapted to engage the actuator linkage so asto move in conjunction therewith.
 4. The vehicle of claim 1, wherein acenterline of the first bore is perpendicular to an axis of rotation ofthe transmission.
 5. The vehicle of claim 1, wherein the apply piston,the return spring, and the actuator linkage are coplanar.
 6. The vehicleof claim 1, further comprising a hard stop within the first bore that isadapted to limit the axial travel of the actuator linkage.
 7. Thevehicle of claim 1, further comprising a pair of collars eachoperatively connected to the actuator linkage; wherein the shift leverengages the actuator linkage between the pair of collars.
 8. The vehicleof claim 1, wherein the VBA is mounted to an underside of the stationarycase.
 9. A rear wheel drive (RWD) automatic transmission having fiveclutches and three gear sets providing a reverse speed and six forwardspeeds including: an engine braking first gear speed, a manual lowspeed, a different first gear speed, and five forward high speeds, theRWD transmission comprising: a center support; a two-mode selectableone-way clutch (SOWC) having a driven member indexed to the centersupport, a rotatable driving member, and a shift lever, the SOWC beingone of the five clutches of the transmission; and a valve body assembly(VBA) positioned adjacent to and below the center support, the VBAhaving an integrated control mechanism adapted to select between the twomodes of the SOWC, and including: a first bore and a second bore,wherein the first bore has a centerline that is positioned below an axisof rotation of the SOWC; an apply piston disposed and moveable withinthe first bore, the apply piston being moveable in a first direction byadmitting pressurized fluid into first bore to thereby select a firstmode of the SOWC, wherein the first mode locks the driving member to thedriven member to allow one of the engine braking first gear speed, themanual low speed, and the reverse speed; a return spring disposed andcompressible within the second bore, and adapted for biasing the applypiston in a second direction to thereby select a second mode of theSOWC, wherein the second mode allows the driving member to freewheelwith respect to the driven member to allow one of the different firstgear speed and the five forward high speeds; and an actuator linkage incontinuous contact with each of the apply piston and the shift lever,the actuator linkage being adapted for moving the shift lever inresponse to a movement of the apply piston within the first bore. 10.The transmission of claim 9, wherein the shift lever extendsradially-outward from the SOWC, and includes a shaped end adapted toengage the actuator linkage so that the shift lever moves in conjunctionwith the actuator linkage.
 11. The transmission of claim 10, wherein theshaped end is configured as a fork, and wherein the actuator linkageincludes a pair of collars between which the fork is positioned.
 12. Thetransmission of claim 11, wherein the shift lever is detachable from theSOWC to facilitate assembly of the transmission.
 13. The transmission ofclaim 9, wherein a centerline of the first bore is perpendicular to anaxis of rotation of the transmission.
 14. A method for reducing spinlosses in a six-speed rear-wheel drive (RWD) automatic transmissionhaving a valve body assembly (VBA) including a hydraulic piston operablefor moving an actuator linkage, and five torque-transmitting mechanismsincluding a two-mode selectable one-way clutch (SOWC) with a shiftlever, the method comprising: positioning the VBA within thetransmission such that a centerline of the hydraulic piston ispositioned below an axis of rotation of the SOWC; determining a shiftcommand signaling a requested shift of the transmission to one of anengine braking first gear speed, a reverse speed, and a manual lowspeed; admitting pressurized fluid into the VBA in response to the shiftcommand to thereby move the hydraulic piston in one direction, and tothereby move the shift lever from a first position to a second position;wherein movement of the shift lever to the second position locks thedriving member to the stationary member.
 15. The method of claim 14,further comprising: determining another shift command signaling arequested shift of the transmission from one of the engine braking firstgear speed, the reverse speed, and manual low speed to one of adifferent first gear speed and a forward high speed; and discharging thefluid from the VBA to thereby move the hydraulic piston in anotherdirection, and to thereby rotate the shift lever to the first position;wherein the first position unlocks the driving member from thestationary member.
 16. The method of claim 15, wherein the transmissionincludes a center support, and wherein the center support is indexed toa case of the transmission.